1. Field of the Invention
This invention relates to a transfer device for generating a regular, linear transfer movement, comprising a fixed housing, a rotatable bar, a slide moving linearly on the bar, guides for controlling the linear movement of the slide, and a follower articulated in the slide and equipped with a tongue, which is elastically stressed in the threaded groove of the bar for transforming the rotational movement of the bar into a linear movement of the slide.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The transfer device described above is suited for example for reading an image plate used in X-raying. In X-raying, the X-radiation conducted through the object and modified by absorption at the object is focused on an activated fluorescent layer in the image plate, where the information contained in the radiation will be stored. After this exposure step the information is read by a laser beam in a separate reading device and is transformed into an image, which is displayed on a computer screen or put out on film. The information is read on an image plate extractable from a cassette, the image plate being in optimally regular linear motion, and after the reading, the plate is cleared of information by means of intense light, and this operation may be performed while the plate is being returned into the cassette to await the following cycle.
FI patent specification 90471 discloses an extractor for reading an exposed image plate extracted from a cassette, in which the plate is moved by a slide gripping it, the slide being moved on a rotatable shaft by means of pulling bearings placed in an ascending angle with the shaft and a separate guide preventing rotation of the slide. Nevertheless, this extractor has involved the problem that the shaft tends to be fouled by oil leaking from the pull bearings and other impurities adhering to the oily shaft. To eliminate this problem, FI patent specification 90472 presents a solution, in which part of the pull bearings placed against the shaft have been replaced with a slide bearing which supports the slide while cleaning the shaft. Nonetheless, as a matter of time, the slide bearing will wear and there will be some play, so that stubborn dirt still gathers on the shaft, interfering with the regular linear movement of the slide and the image plate on this and deteriorating the quality of the image to be read.
FI patent application 940204 describes a further enhanced transfer device for reading an image plate used in X-raying, which corresponds to the above definition of the object of the present invention. Thus, the shaft of the transfer device described in patent application 940204 consists of a threaded bar, whose rotational movement is transformed into a linear movement of the slide which moves the image plate to be read by means of a follower, which is elastically stressed in the threaded groove of the bar. The follower is a plate-like body articulated in the slide and stressed in the bar groove under the effect of a magnet. The transfer device provided with such a follower has the advantage of a straightforward design and of the follower continuously cleaning the threaded groove in the bar, whose operation will not be basically affected by wear. In this manner, the slide will retain its linear movement and the quality of the images to be read will persist even when used over a long period of time.
Moreover, the magnetically stressed follower in FI application 940204 has the property of giving way to any irregularities or impurities in the threaded groove of the bar by yielding in the transverse direction of the bar, and as the follower moves away from the bar in the basically V-shaped groove, the linear movement of the slide is slowed down. However, the magnetic force decreases simultaneously as a result of growing distance, so that the stress exerted by the follower on the bar is relieved, and at the same time the rotational movement of the bar and accordingly the linear movement of the slide accelerate. Thus, these processes compensate each other at least partly so as to favour the continuously regular movement of the slide. If, however, there is some curvature in the threaded bar, the position and the loading force of the follower in the transfer device of FI patent application 940204 will be altered in the long term so that the rotational movement of the bar and the consequent linear movement of the slide will not remain constant over the entire length of the slide path, but gradual changes will occur. This causes a problem especially when the paths of the bar and the moving slide are long.
The object of this invention is to further enhance the transfer device for generating a regular linear movement so as to provide a device which is even less sensitive to irregularities or dirt or other impurities in the threaded groove of the bar, and which also keeps the linear movement of the slide constant regardless of any curvature in the threaded bar.